A report published in February 1997 by Sandia National Laboratories entitled “Cost Analysis of Energy Storage Systems for Electric Utility Applications” contains a summary of the developments and the potential that energy storage systems of differing types have. Excerpts from that report are as follows:
“Energy Storage (ES) systems could potentially have widespread applications within the electric utility industry. Three promising storage technologies—Battery Energy Storage (BES), Superconducting Magnetic Energy Storage (SMES) and Advanced Flywheel Energy Storage (FES)—each meet some of the performance requirements of the 13 utility applications identified in the Battery Energy Storage for Utility Applications: Phase I—Opportunities Analysis study conducted by Sandia National Laboratories (SNL).”
“Both in terms of performance and cost, BES and SMES are well suited for power quality applications. Fast acting advanced FES also has the potential to serve this application and prototypes have been demonstrated. SMES and FES systems are in the early stages of market entry and are expected to primarily serve the customer-end power quality market.”
There are typically three key components of ES systems, namely:                Storage Subsystems;        Power Conversion Subsystems (PCS); and        Balance of Plant (BOP).        
From the above-identified report, it is known that the storage subsystem of a FES consists of a flywheel that stores kinetic energy by spinning at very high velocities (tens of thousands of revolutions per minute). The FES also consists of the radial and thrust magnetic bearings, centre post, containment and other components.
The power conversion subsystem for all three abovementioned subsystems includes a combination of rectifier/inverter, transformer, DC and AC switchgear, disconnects, breakers, switches and programmable high-speed controllers. A high speed motor/generator set is part of the power conversion system in the FES system. High speed solid-state transfer switches are used in power quality applications where high switching speeds are a requirement for the ES system.
The control system for ES systems has three main functions. The management and control of storage subsystem monitors the charge level, charge/discharge requirements, and related operations. The controls associated with the PCS subsystems monitors utility power supply and switches the load between the ES system and utility supply according to a predetermined algorithm. The facility control system monitors the temperature, ventilation and lighting in the facility that houses the hardware.
The balance of plant encompasses the facility to house the equipment, heating, ventilation and air conditioning (HVAC), the interface between the ES system and the customer/utility, the provision of services such as data gathering/trending, project management, transportation permits, training, spares and finance charges.
Prior art FES systems have been used mainly for automotive and space applications and have yet to become accepted due to their complexity, low net power output and fragility in operating conditions. For example, for automotive applications, dynamic isolation problems are present. Though the concept of flywheels is not new, low-loss flywheels that rotate at very high speeds are relatively new and undeveloped.
A typical prior art centrifugal clutch consists of three parts:                An outer drum that turns freely—this drum includes a sprocket that engages the chain. When the drum turns, the chain turns.        A centre shaft attached directly to the engine's crankshaft—if the engine is turning, so is the shaft.        A pair of cylindrical clutch weights attached to the centre shaft, along with a spring that keeps them retracted against the shaft.        
The centre shaft and weights spin as one. If they are spinning slowly enough, the weights are held against the shaft by the spring. If the engine spins fast enough, however, the centrifugal force on the weights overcomes the force being applied by the spring, and the weights are slung outward. They come in contact with the inside of the drum and the drum starts to spin. The drum, weights and centre shaft become a single spinning unit because of the friction between the weights and the drum. Once the dram starts turning, so does the chain.
There are several advantages to a centrifugal clutch:                It is automatic. (A centrifugal clutch does not use a clutch pedal for engagement and disengagement.)        It slips automatically to avoid stalling the engine. (In a car, the driver must slip the clutch.)        Once the engine is spinning fast enough, there is no slip in the clutch as the faster the engine is travelling, the greater the force exerted on the engagement.        
Centrifugal clutches are typically used in automotive applications. As such, they are generally mounted horizontally. There are a variety of problems present in adapting the conventional centrifugal clutch to use in flywheel energy storage systems as will become apparent from the following discussion.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.